1. Field of the Invention.
The present invention relates to a control system particularly for use with fluorescent lights and, more particularly, to an initialization circuit which operates to delay the application of a signal calling for dimming of a fluorescent light for a predetermined time period.
2. Reference to Other Applications
Two other U.S. patent applications Nos. 239,209 and 246,952, in the names of the present inventors and assigned to the present assignee entitled "Power Control Circuit for Inductive Loads" and "Notch Cutting Circuit with Minimal Power Dissipation," respectively, have been filed on even date herewith, and disclose and claim circuitry useful in cooperation with the present invention.
3. Description of the Prior Art.
In a co-pending application Ser. No. 898,569 filed Aug. 21, 1986, in the name of L. S. Atherton, R. A. Black, Jr., and A. D. Kompelien, and assigned to the assignee of the present invention, a circuit is described which provides fluorescent light dimming by creating a "notch" and controlling the width and position thereof along the alternating waveform produced by the power supply which energizes the fluorescent light. In this co-pending application, the power to the inductive ballast of a fluorescent light is interrupted for a short period of time on both the positive and negative half cycles of the power supply so as to provide a waveform with a "notch" in each half cycle. The position and width of these "notches" operate to vary the power supplied to the ballast and thus provide the desired dimming.
It has been discovered that upon starting the system after it has been "off" for a period of time with the signal calling for dimming of the fluorescent light, the life of the fluorescent light is undesirably shortened. This is because the filament or cathode of the tube needs at least ten to fifteen seconds to warm up before it can properly accept a signal calling for dimming of the fluorescent light. Applying a dimming signal too early after the initial starting thereof causes undue wear on the light and shortens its life.
It would be desirable to always initially start the fluorescent light control system in a "full on" condition for a predetermined period of time sufficient to allow the filament to become fully activated before producing the dimming control signal. It is also desirable to wait a couple of seconds before applying even the "full on" signal so as to allow stabilization of the electronic components in the control circuitry.